1. Field of the Invention
The present invention relates to an ink jet recording apparatus provided with an ink supply route having a deaerator therefor. The invention also relates to an apparatus for manufacturing color filters that manufactures color filters by coloring a transparent substrate with ink by use of such ink jet recording apparatus.
2. Related Background Art
The ink jet recording method has conventionally been adopted as output means of information processing systems, such as a printer serving as the output terminal of a copying machine, a facsimile equipment, an electronic typewriter, a word processor, or a work station or it has been adopted conventionally as the recording method of a handy or a portable printer provided for a personal computer, a host computer, an optical disc device, a video apparatus, or the like.
The ink jet recording method is used for recording characters, figures, and the like by discharging fine ink droplets from nozzles (hereinafter referred to as discharge ports). This method has excellent advantages in the output of highly precise images as recording means executable at higher speeds. Also, the recording apparatus to which the ink jet recording method is applicable (hereinafter referred to as an ink jet recording apparatus) is of non-impact type, and makes a lesser amount of noises when operated. Also, it is easier for the apparatus to use ink of many colors for recording color images. Further, among some other advantages, the apparatus main body can be made smaller and easier to provide highly densified images. With such wider use, the ink jet recording method has rapidly been in demand increasingly more in recent years.
Also, along with the development of personal computers, particularly the portable personal computers, there has been a tendency that the liquid crystal display, particularly its color display, is in demand more in recent years. However, in order to popularize the use of this type of display more widely, it is necessary to reduce its costs of manufacture. Particularly, the reduction of costs is demanded more on the color filters, because they cost high.
There have been attempted various methods in order to meet such demand on the cost reduction, while maintaining the required characteristics of color filters satisfactorily. However, no method has been established as yet to satisfy all the requirements in this aspect. Now, hereunder, the description will be made of some of the methods for manufacturing color filters; here, R, G, B stand for red, green, and blue in the description given below.
There is the dyeing method as a first method for manufacturing color filters. The dyeing method is such that on the glass substrate, water soluble polymer material is coated for use of dyeing, and that after patterning the water soluble polymer material to a desired configuration by means of photolithographic process, the pattern thus obtained is immersed into the dyeing bath. In this manner, the colored pattern is obtained. By repeating this process three times, the R, G, B color filter layers are produced on the glass substrate.
There is the pigments dispersion method as a second method for manufacturing color filters. The pigments dispersion method has almost taken place of the dyeing method in recent years. The pigments dispersion method is such that pigments are dispersed on the substrate to form a photosensitive resin layer, and that by patterning this photosensitive rain layer, a monochrome pattern is obtained. Then, by repeating this process three times, the R, G, B color filter layers are formed on the substrate.
There is the electrodeposition method as a third method for manufacturing color filters. The electrodeposition method is such that on the substrate, transparent electrodes are patterned, and then, the substrate is immersed in the electrodeposition coating agent that contains pigments, resin, and electrolytic solution, among some others, thus electrodepositing a desired color on the substrate. By repeating this process three times, R, G, B are separately coated on the substrate, and after that, resin is thermally hardened to form the surface color layer on the substrate.
There is the printing method as a fourth method for manufacturing color filters. The printing method is such that pigments are dispersed on the thermally hardening resin, and printing is repeated three times using such resin for the separate coating of R, G, B. After that, resin is thermally hardened to form color layers on the substrate. Also, it is generally practiced to form a protection layer on the surface of the color layer produced by any one of these methods described above.
The processing aspect that shared by these methods is the need for the three-time repetition of one and the same process for coloring in R, G, B, which inevitably results in the higher costs. Then, there is a problem that the more the processes are needed, the more production yield is reduced. Further, for the electrodeposition method, the formable pattern configuration is automatically limited. Therefore, the techniques currently in use for this method is not applicable to manufacturing the color liquid crystal display of the TFT type. Also, with the printing method, the resultant resolution and smoothness are not good enough to form patterns at fine pitches.
In order to compensate for these drawbacks, a method for manufacturing color filters with an ink jet recording method is proposed as disclosed in the specification of Japanese Patent Laid-Open Application No. 59-75205, Japanese Patent Laid-Open Application No. 63-235901, Japanese Patent Laid-Open Application No. 63-294503, or Japanese Patent Laid-Open Application No. 1-217302, among some others.
Of these methods disclosed in them, the method for manufacturing color filters by means of the ink jet recording method is typically such that a light shielding film is provided to form apertures on the transparent substrate with a specific regularity, and that ink is discharged from the ink jet head for coloring on the transparent substrate having such exposed apertures on it.
The material costs of the color filters produced by use of the ink jet recording method can be made lower, because coloring is given only on the parts that require it. Moreover, it is possible to provide the three colors at a time. The required time for manufacturing steps is shorter to make it easier to avoid influences that may be exerted by the presence of dust particles. Also, the costs of manufacturing system can be made lower. As a result, the lower material costs and the higher production yields can be anticipated for the reasons described above, among some others, and as compared with the other methods of manufacture, it is possible to manufacture color filters at lower costs by use of the ink jet recording method.
FIG. 11 is a view which schematically shows the structure of the ink supply system of the conventional ink jet recording apparatus. As shown in FIG. 11, the ink supply system of the conventional ink jet recording apparatus comprises an ink jet heat 1100; a sub-tank 1401 retaining ink to be supplied to the ink jet head 1100; and a main tank 1301 retaining ink to be supplied to the sub-tank 1401.
On the inner bottom surface of the main tank 1301, the one end of a tube 1351 is arranged, and the other end of the tube 1351 is connected with one end of a tube 1352 outside the main tank 1301 through a main pump 1302. On the portion of the tube 1351 near the main tank, one end of a tube 1355 is connected for use of the air communication through a joint 1371. The other end of the tube 1355 is connected with one end of a tube 1356 for use of the air communication through a two-way valve 1304. When the two-way valve is open, the air outside and the tube 1351 are communicated through the other end of the tube 1356 by way of the tubes 1356 and 1355. In FIG. 11, the two-way valve is in the state of being closed.
On the other hand, one end of a tube 1353 is connected with the other end of the tube 1352 through a reverse flow prevention valve 1303. To the other end of the tube 1353, one end of a tube 1453 and one end of a tube 1452 are connected through a joint 1471. The other end of the tube 1453 is connected with one end of a tube 1454 in the vicinity of the sub-tank 1401 through a two-way valve 1403, while the other end of the tube 1454 is communicated with the interior of the sub-tank 1401. The ink supply from the main tank 1301 to the sub-tank 1401 is made through the tubes 1351, 1352, 1353 and 1454. Then, by means of the two-way valve 1403, the ink supply route is closed or opened between the main tank 1301 and the sub-tank 1401.
For the sub-tank 1401, there are arranged a turbine 1402a that rotates on the bottom in the interior of the sub-tank 1401, and a motor 1402 that drives the turbine 1402a. Near the portion where the turbine 1402a is provided for the sub-tank 1401, one end of a tube 1451 is connected, and the other end of the tube 1451 is connected with an air buffer 1501. When the turbine 1402a is driven, ink in the sub-tank 1401 is compressed and carried to the air buffer 1501 through the tube 1451.
Also, from the side wall of the sub-tank 1401, an exhaust drain 1404, which is communicated with the interior of the sub-tank 1401, is extended, and one end of a tube 1354 is connected with the leading end of the exhaust drain 1404. The other end of the tube 1354 is led into the main tank 1301. With the exhaust drain 1404 arranged at a specific height from the bottom end of the sub-tank 1401, ink in the sub-tank 1401 is exhausted from the exhaust drain 1404 at a predetermined liquid level. Ink thus exhausted from the exhaust drain 1404 returns through the tube 1354 to the interior of the main tank 1301 from the other end of the tube 1354.
On the bottom end of the air buffer 1501, each end of tubes 1551 and 1553 is connected, respectively. The other end of the tube 1551 is connected with the ink supply route in the ink jet head 1100 through a connector 1102. On the other hand, the other end of the tube 1553 is connected with a three-way valve 1502. Then, one end of a tube 1552 and one end of a tube 1554 are connected with the three-way valve 1502. In FIG. 11, the tube 1553 and the tube 1552 are joined by means of this three-way valve 1502. The other end of the tube 1552 is connected with the ink supply route in the ink jet head 1100 through a connector 1102. This connector 1102 enables the ink jet head 1100 to be detachably connected with the ink supply system. When the ink jet head 1100 should be replaced with another one, the ink jet head 1100 can be removed from the ink supply system in this portion the connector 1102. On the ink jet head 1100, discharge ports 1100a are formed, and ink is supplied to these discharge ports 1100a from the ink supply route in the ink jet head 1100.
Also, to a position of the side wall of the air buffer 1501 at a predetermined height, one end of a tube 1555 is connected. The other end of the tube 1555 is connected with one end of the tube 1556 through a two-way valve 1503. The other end of the tube 1556 is connected with the other end of the tube 1554 and the other end of the tube 1452 described earlier by way of a joint 1571. In this manner, the ink supply route is structured so that even if vibration is given to the ink supply system due to the movement of the ink jet head 1100 in the scanning directions, such influence may be exerted on the ink supply system by the vibration is not allowed to reach the ink jet head 1100 side. Thus, the discharges of ink from the discharge ports 1100a are prevented from becoming instable so as to generate density unevenness or the like.
FIG. 12 is a partly enlarged view which shows the ink supply system represented in FIG. 11. Now, with reference to FIG. 12, the description will be made of the operation of the conventional ink supply system of an ink jet recording apparatus.
When the usual printing is performed, ink 1100b is discharged from the discharge ports 1100a of the ink jet head 1100 as flying liquid droplets as shown in FIG. 12. Then, negative pressure is exerted in the interior of the ink supply route of the ink jet head 1100. With this negative pressure of ink in the ink jet head 1100, ink in the sub-tank 1401 is supplied to the ink jet head 1100 through the tube 1451, the air buffer 1501, and the tube 1551. Also, a part of ink in the interior of the air buffer 1501 is branched into the tubes 1553 and 1552 and supplied to the ink jet head 1100. With ink thus supplied, ink jet head 1100 discharges ink from the discharge ports 1100a for recording on a recording medium. In this case, if bubbles are mixed in ink, the bubbles are trapped when passing the air buffer 1501 to let them reside on the upper part of the air buffer 1501. In this way, the bubbles in ink are removed so that the ink jet head 1100 may prevent its defective discharges from being caused by the presence of the bubbles.
Now, of the conventional ink jet recording apparatuses, the description will be made of the one which uses the deaerator.
As the method for stabilizing the ink discharges of an ink jet recording apparatus, there are known some methods whereby to remove the dissolved gas residing in ink to be supplied to the ink jet head. Of such methods, the one is disclosed in the specification of Japanese Patent Laid-Open Application No. 5-17712 for removing the dissolved gas residing in ink by allowing it to pass a film having a gas permeability. In accordance with such specification thus disclosed, the effect obtainable by deaerating ink in an ink jet recording apparatus that uses a piezoelectric elements is such that no cavitation occurs even if ink in the compression chamber is abruptly compressed repeatedly, and that no defective printing is caused to ensue by disabled ink discharges due to cavitation. As the ink deaerator, the film having the gas permeability is produced in the form of a tube, and at the same time that evacuation is effectuated outside such tube. Then, ink is allowed to pass the interior of the tube, In this manner, the dissolved gas in ink is removed to the outside of the tube, hence deaerating ink. As the use condition of such deaerator, the degree of vacuum is 1 atm (76 Torr) or less outside the tube. However, there is no particular reference made as to the level of the deaerated ink after having passed the deaerator.
Also, for the ink jet recording method that utilizes film boiling for discharging ink, it has been confirmed that ink deaeration is effective. As the confirmed effect on such deaeration, it is known that with the supply of deaerated ink to the ink jet head, the bubbles that may cause defective discharges can be prevented from being carried into the ink jet head.
For an ink jet recording apparatus capable of deaerating ink, there are known structures (such as disclosed in the specifications of Japanese Patent Laid-Open Application No. 57-83488 and Japanese Patent Laid-Open Application No. 62-288045) in which an ink tube is formed by flexible plastic material having an excellent ink resistance on the inner surface exposed to ink, which is arranged on the ink supply route from the ink tank to the ink jet head, and then, this tube is covered by a material whose air permeability is small. More specifically, it is conventionally regarded as the most suitable structure that a plastic material having softness is always used for an ink supply tube in order to make it possible for the ink jet head to move, and then, the polyethylene inner tube is externally covered by polyvinylidene chloride.
However, when an ink jet head is used for a color filter manufacturing apparatus, there is a need for the enhancement of its shooting accuracy almost by one digit higher than that of the printer generally in use, because unlike the case where the ink jet head is used for a usual printer, coloring should be made on the transparent substrate by discharging ink from the predetermined discharge ports which are arranged with strict regularity. Therefore, the color filter manufacturing apparatus is structured differently from the usual ink jet recording apparats. It is generally practiced for the usual ink jet recording apparatus to record images by discharging ink to a recording medium, while causing the ink jet head to scan forward and backward in the direction at right angles to the carrying direction of the recording medium. On the other hand, the ink jet head is fixed for the color filter manufacturing apparatus, because it is required for the ink jet head to secure highly precise positions for the performance of its discharges. Then, ink is discharged from the ink jet head, while the transparent substrate mounted on the stage being scanned in the X-Y directions underneath the fixed ink jet head.
Also, for the conventional ink jet recording apparatus, the air buffer is provided for the ink supply system thereof as shown in FIG. 11 and FIG. 12 which illustrate the conventional techniques. With the air buffer, it is made possible to eliminate any influence that may be exerted by the vibration generated by the movement of the ink jet head in the scanning directions. Then, it is attempted to stabilize the ink discharges, and at the same time, to prevent defective discharges of the ink jet head from being caused by the creation of bubbles in ink by trapping them for removal when ink passes the air buffer if any bubbles are mixed in ink.
However, as described earlier, for the color filter manufacturing apparatus that uses the ink jet head, the ink jet head is fixed and does not scan in order to obtain higher precision. Therefore, unlike the usual ink jet recording apparatus, there is no possibility that the vibration generated in the ink supply system due to the movement of the ink jet head in the scanning directions exerts any influence on ink discharges. Also, for the conventional system, ink in the ink supply route is pressurized to circulate it in the ink supply route by means of the turbine or the like serving as ink supply means in order to keep the amount of air constantly in the air buffer or to perform the recovery operation for the ink jet head. The operation to pressurize ink at that time is such as to act upon the air residing on the upper part of the air buffer to be dissolved into ink pressured by ink supply means. Then, the ink into which the air is dissolved is supplied to the ink jet head. As a result, the air dissolved in ink is extracted in the tubes between the air buffer and the ink jet head after a specific time has elapsed. Therefore, ink may be supplied to the ink jet head, in some cases, together with the dissolved air which is in the state of being extracted from ink.
Also, when color filters are manufactured, ink currently used for the color filter manufacturing apparatus should be replaced with some other ink having different density or different color itself in order to change the colors of the color filter minutely. In this case, it is necessary for the conventional ink supply system of the color filter manufacturing apparatus to draw out ink current in use from the ink supply route completely. After that, new ink is filled in the ink supply system. When such new ink is filled in the system, the ink jet head 1100 should be removed from the connector 1102 shown in FIG. 11. Then, a bypass jig is mounted on the connector 1102, instead of the ink jet head 1100, in order to bypass the ink supply route for filling new ink. When new ink is filled, the bypass jig is removed from the connector 1102, and then, the ink jet head head 1100 is fixed to the connector 1102 again. Here, however, when the ink jet 1100 is again fixed, the air is always mixed in the interior of the connector 1102. The air once mixed is carried over into the interior of the ink jet head 1100 eventually, and in some cases, it may cause the disabled ink discharges or the defective ink discharges. Further, in order to exhaust the air mixed in the ink supply route immediately close to the ink jet head 1100, it is arranged to supply ink by the ink supply means so that the air is pushed out from the discharge ports 1100a of the ink jet head 1100. In this case, ink is forcibly pushed out from the discharge ports 1100a. Then, a problem is created that ink is wastefully consumed.
Now, for an ink jet recording apparatus capable of deaerating ink, there are known structures (such as disclosed in the specifications of Japanese Patent Laid-Open Application No. 57-83488 and Japanese Patent Laid-Open Application No. 62-288045) in which an ink tube is formed by flexible plastic material having an excellent ink resistance on the inner surface exposed to ink, which is arranged on the ink supply route from the ink tank to the ink jet head, and then, this tube is covered by a material whose air permeability is small. More specifically, it is regarded as the most suitable structure conventionally that a plastic material having softness always used for an ink supply tube in order to make it possible for the ink jet head to move, and then, the polyethylene inner tube is externally covered by polyvinylidene chloride.
However, when an ink jet head is used for a color filter manufacturing apparatus, there is a need for the enhancement of its shooting accuracy almost by ten times higher than that of the printer generally in use, because unlike the case where the ink jet head is used for a usual printer, coloring should be made on the transparent substrate by discharging ink from the predetermined discharge ports which are arranged with strict regularity. Therefore, the color filter manufacturing apparatus is structured differently from the usual ink jet recording apparats. It is generally practiced for the usual ink jet recording apparatus to record images by discharging ink to a recording medium, while causing the ink jet head to scan forward and backward in the direction at right angles to the carrying direction of the recording medium. On the other hand, the structure is adopted for the color filter manufacturing apparatus in which the ink jet head is fixed in order to meet the required precision, and then, ink is discharged from the ink jet head to the transparent substrate (recording medium) mounted on the stage that the head faces, while the substrate being scanned in the X-Y directions.
Since the extremely high precision is required for the color filters, it is easier for them to be defective as the finished product if the amount of discharged ink varies even slightly, because the difference in the amount of ink looks like streak unevenness on the transparent substrate when the ink jet recording method is used for the color filter manufacturing apparatus. Therefore, there is a need for the provision of much higher stability of the discharge amount than for the usual ink jet printer. In this respect, as a result of ardent studies as to the prevention of the unevenness that may be brought about by the fluctuation of the discharge amount, the inventor hereof has found that the deaerators incorporated on the way with the ink supply route of the ink jet head used for the color filter manufacturing apparatus may significantly contribute to reducing the generation of the aforesaid unevenness.
However, the color filter manufacturing apparatus is much larger than the usual ink jet printer, and also, the ink supply unit, such as ink tanks, should be structured outside the main body that includes the X-Y stage and the like. Therefore, the length of ink supply tubes that connect the ink tanks with the ink jet head becomes as long as several meters eventually. Also, for the color filter manufacturing apparatus, the ink jet heads are mounted on the apparatus to cover the three color portions of RGB, and each color ink jet head of those mounted on the apparatus should be provided with nozzles for use of ink discharges with the positional precision of in order of one .mu.m or less. This requires highly precise positioning for each of them. Therefore, on the portion where ink jet heads are installed, the mechanism to adjust the position of each of the ink jet heads is arranged accordingly. In order to make the stability of ink discharges more effective by means of deaeration, it is desirable to arrange each of the deaerators immediately before each of the ink jet heads so that the deaerated ink should be supplied to the ink jet heads in the shortest possible distance without allowing the deaerated ink to run around in a considerable distance. However, for the reasons that the adjustment mechanism should be provided for each of the ink jet heads, and the arrangement of anything that has weight should preferably be avoided around such adjustment mechanism needed for securing higher precision, among some other reasons, it is impossible to arrange the deaerators by the side of each of the ink jet heads. Consequently, it is inevitable that the tubes become longer to supply ink from each of the deaerators to the ink jet head when the deaerators are incorporated with the apparatus.
Also, it is desirable to select the material of the tubes to supply ink to each of the ink jet head taking the gas permeability into consideration. In general, the gas permeability of tube is smaller when the thickness thereof is larger. As in the conventional case where resin such as polyethylene having excellent resistance to ink is used for the inner side of the tube, which is externally covered by polyvinylidene chloride, the gas permeability of such tube is determined almost by the thickness of polyvinylidene chloride. Therefore, if such tube is adopted for the ink supply route between each of the deaerator of the color filter manufacturing apparatus and the ink jet heads, the concentration of dissolved gas in ink tends to be increased, because the thinner polyvinylidene chloride together with the longer tube may admit the transmission of gas through the tube wall before the tube reaches each ink jet head, thus the gas that has transmitted the tube wall is dissolved into ink. Also, when ink jet heads are replaced, which necessitates the shifting of ink supply tubes, the resin cover whose gas permeability is smaller tends to be peeled off when the tubes are rubbed each other. Thus, there is a possibility that the tubes do not present sufficient resistance to the gas permeability eventually.
The inventor hereof has found that there is a need for supply deaerated ink to the head more effectively in order to carry out the production of color filters more stably, and also, means should be arranged so as not to lower the deaeration level of ink before ink reaches the ink jet heads from the respective deaerators.